I know this is a little late seeing as how this post was created almost eight years ago, but to answer the question...the suffix -rin itself is very similar to the suffix -kun; it usually means that one is being deemed a close friend. However, -rin has a much more female connotation than -kun. It is also usually conveniently applied to names which already end in -ri, like Kofuku changing Hiyori's name to Hiyorin in Noragami, because it was just that easy.